Abstract: The goal of this proposal is to elucidate the molecular mechanisms governing BubR1 protein abundance and function, and its role in the regulation of tumorigenesis and aging. Aging is the single greatest risk factor for cancer development, yet the mechanistic basis driving this interrelationship remains largely undefined. BubR1, a serine/threonine protein kinase, is involved in the spindle assembly checkpoint (SAC) to ensure faithful chromosome segregation during mitosis, and therefore is intimately linked to genomic integrity and cancer. Interestingly, recent studies have implicated BubR1 in the aging process where BubR1 abundance has been shown to decline in a variety of tissues as mammals age. Mice engineered to express low levels of BubR1 from birth die within a year, exhibiting increased senescence, premature aging phenotypes and an increased susceptibility to cancer, whereas mice overexpressing BubR1 have an extended lifespan with reduction in age- related diseases and cancer development. Senescence is believed to be largely tumor-suppressive and prevent cancer in young individuals. However, in aged individuals senescent cells can contribute to age-related cancer development. Therefore, BubR1 may play a pivotal role in the interrelationship between aging and cancer given that BubR1 suppresses both senescence and tumorigenesis. Previously, we identified an acetylation-dependent mechanism regulating BubR1 protein stability, where SIRT2 prevents degradation of BubR1 through deacetylation, leading to lifespan extension of a BubR1 premature aging mouse model. Furthermore, BubR1 protein levels in aged animals can be restored to youthful levels by stimulating SIRT2 activity through induction of NAD+ levels. These results suggest that the age-related decline in BubR1 levels can be reversed, potentially alleviating age-related diseases including cancer. Therefore, we hypothesize that BubR1 is a key tumor suppressor, and its loss with age increases cancer susceptibility. In this proposal, we plan to: 1) elucidate the physiological role of BubR1 post translational modifications during aging and calorie restriction and their impact on mitotic progression and tumorigenesis; and 2) determine the mechanisms regulating BubR1 protein abundance and function during aging. These studies will elucidate how regulation of BubR1 by post-translational modifications controls mitotic progression and tumorigenesis during aging as well as to identify mechanisms through which BubR1 declines with age and controls the aging processes. Given that aging poses the largest single risk factor for developing cancer, elucidating the molecular details governing the physiological role of BubR1 in cancer and aging will provide mechanistic understanding of the interrelationship between aging and cancer development, as well as identify possible therapeutic strategies to treat age-related diseases.